Step 1: What you need
wheels for the forks
A piece of 10' steel electrical conduit that can fit (snuggly-ish)over the head of the bike fork. 1" conduit worked for me
A piece of thinner conduit, also steel. This is to make a brace or two
A sturdy piece of wood. I initially used a broomstick, which prompty shattered. A 2x3 worked (and is still working...)
Two old bike inner tubes. Get these from the dumpster behind a bike store, or your enemies' bikes
the plumbing pipes in the picture have nothing to do with the project--they're just living their lives, not bothering anybody, so I say, live and let live, right?
Step 2: Ways to build it
The differences are how you attach the bits of conduit to one another.
Lash with inner tubes
I used a MIG welder, because I wanted welding practice. If you wanted to bolt instead, every time I weld two pieces together, you would drill a hole through them and stick a bolt through it. You'll probably want to whack the conduit a bit where you'll be drilling to flatten it out.
If you're lashing, then just lash, man.
THIS IS REALLY IMPORTANT!
If you're welding, be sure that you don't have galvanized conduit. Seriously--welding galvanized steel frees criminal molecules that had been locked up in their metallic prison, and the criminal molecules run through the air into your lungs and try to kill you. So seriously, don't weld galvanized stuff.
also, if you're welding, make sure all your conduit is steel. Otherwise it probably won't work.